1. Field of the Invention
The present invention relates to a resonance type solid-state imaging element including an imaging region in which a plurality of pixels are provided on a semiconductor substrate and a peripheral circuit region for driving the plurality of pixels and a method for manufacturing it.
2. Related Art
There is a demand for realization of MOS (Metal Oxide Semiconductor)-type solid-state imaging elements which bring cameras for night security, cameras boarded on safety driving assisting automobiles, and the like to have high sensitivity to, in addition to light in the visible region, light in the near-infrared region having a wavelength longer than that in the visible region. The MOS-type solid-state imaging elements are image sensors that read out signals accumulated in PN photodiodes forming pixels by using amplifier circuits included in MOS transistors and have features of being operated at low voltage and of being capable of high-speed reading and capable of being incorporated with peripheral circuits composed of MOS transistors in a single chip. However, silicon, which has been widely used as a semiconductor material for the solid-state imaging elements, hardly absorbs light having a wavelength exceeding approximately 1100 nm owing to its physical limit, and therefore, it is difficult to provide sensitivity to light having such a long wavelength to an image sensor using a silicon substrate. Further, image sensors using a silicon substrate have an optical absorption coefficient depending on the wavelength to have low sensitivity to light of which wavelength is in the near-infrared region exceeding 800 nm when compared with that to light of which wavelength is in the visible region. As a countermeasure against this problem, a resonance type light receiving device as a single light receiving element has been known which reflects light made incident from the obverse face of a substrate, on which the pixels are provided, on the reverse face thereof to increase the quantum efficiency, thereby increasing the sensitivity to longer-waveform light. As a conventional technique of this kind, Japanese Unexamined Patent Application Publication 2005-175142 will be referred to.
A substrate 1001 used in the conventional resonance type light receiving device is formed in such a fashion that the reverse face of a substrate on which elements are to be formed is joined to a silicon oxide film 1010 (forming a part) of another substrate, as shown in FIG. 18. Further, for efficient photoelectric conversion of incident light from the obverse face of the substrate, a recess 1122 is formed by etching a reverse face portion of the substrate 1001 in the light receiving region with the use of the silicon oxide film 1010 as a stopper layer. A reflective film 1117 mainly made of metal is formed on the reverse face of the substrate 1001. With this structure, the conventional resonance type single light receiving device utilizes the resonance effect that light made incident from the obverse face of the substrate is reflected on the reverse face thereof and the thus reflected light is further reflected on the obverse face thereof, thereby increasing the quantum efficiency.
In general, however, the substrates bonded to each other by means of the silicon oxide film (hereinafter referred to it as an SOI (Silicon on Insulator) substrate is higher in manufacturing cost and cost of the resultant product than an ordinary substrate made of only silicon (hereinafter referred to it as a silicon substrate).